Direct access storage device with magneto-resistive transducing head apparatus and a common read return signal line

ABSTRACT

A direct access storage device includes at least one disk mounted for rotation about an axis and having opposed disk surfaces for storing data. A magneto-resistive (MR) transducer head is mounted for movement across each respective disk surface for writing to and for reading data signals from the disk surface. Each MR transducer head includes a write element and a read element. A preamplifier, associated with the MR transducer head, amplifies read and write signals of the read element and the write element. A flex cable couples the read and write signals between the preamplifier and the MR transducer heads. The flex cable includes a common read return signal line for each sequential pair of the MR transducer heads.

This application is a continuation of application Ser. No. 08/646,904,filed May 8, 1996, now abandoned. Which is a divisional of applicationSer. No. 08/347,536 filed on Nov. 30, 1994 now U.S. Pat. No. 5,552,950.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a direct access storagedevice (DASD) and more particularly to a magneto-resistive transducinghead signal apparatus used in a DASD.

2. Description of the Prior Art

Various types of storage units, such as direct access storage devices(DASDs) are used to store data for known data processing systems. Oneoften used type of DASD is a magnetic disk unit including a number ofdisks having surfaces with magnetic active material onto which data iswritten and from which data is read by magnetic read/write heads. Inother types of DASDs, optical or other data storage media may beemployed.

In a magnetic disk unit, the disks are formatted to define sectors andtracks upon the disk surfaces. Tracks are usually circular regionscoaxial with the disk axis where data may be written, and sectors areparts of the tracks capable of storing a predetermined quantity of datawritten to the disk. Axially aligned tracks on the disks of a DASD arereferred to as cylinders. The sectors of a DASD where blocks of data arestored have unique physical data block addresses (DBA). The disks of theDASD spin in unison around a common axis, and the transducer heads,usually one for each surface, are moved radially in unison across thedisk surfaces. When data is read from or written to a physical DBA, theheads are moved into alignment with the cylinder containing the track inwhich the DBA is found, and the data transfer takes place as the sectoror sectors of the DBA spin under the head.

Magneto-resistive (MR) transducer heads provide a significantadvancement in read/write technology for DASDs. The magneto-resistiveeffect is a physical effect observed in certain materials, wherebyelectrical resistance of the material changes as it moves through amagnetic field. This effect can be used to read data recorded on thesurface of a magnetic disk. The recorded data bits are in effect tinymagnets which create small magnetic fields near the disk surface. A readelement comprising a magneto-resistive material flies in close proximityto the disk surface, varying the resistance of the element. Since avariable resistance can be detected with some electrical current flowingthrough the resistive element, the selected MR read element has a biascurrent flowing through the element as the head flies over disk surface.A preamplifier amplifies a change in voltage related to the change inresistance of the read element, and this is ultimately translated todata.

The chief advantage of the MR transducer head over conventionalinductive head technology is that the MR read element is considerablymore sensitive to small magnetic fields than an inductive element,enabling higher data recording densities. The MR transducer headincludes separate read and write elements because the magneto-resistiveeffect cannot be used to write data on the disk surface. The writeelement, which is a conventional inductive element, is used for writingdata.

FIG. 4 illustrates a conventional arrangement for connection of two MRtransducer heads in a DASD. Each MR transducer head requires four signalwires. Two signal wires are used to carry write current to the writeelement and two signal wires are used to carry read current from the MRread element.

MR heads provide a very low amplitude signal. Picking up unwanted noisein the electrical signal path can cause signal degradation. Apreamplifier is used early in the electrical signal path to amplify theread current and the write current. In some known DASDS, thepreamplifier advantageously is positioned off the actuator at astationary location. Keeping the preamplifier off the actuator minimizesactuator mass to speed up access time. As shown in the prior artarrangement of FIG. 4, providing a stationary preamplifier requires theflex cable to carry the MR signal lines.

Disk drive dimensions are normally limited by a form factor, an industrystandard of length, width and height dimensions. As disk drive deviceform factors become increasingly smaller, electrical connections to theusing system can utilize an increasingly greater portion of the deviceform factor. With some form factors, the number of signal lines requiredfor use with MR transducer heads would exceed the allowable space forthe flex cable.

A need exists to provide an improved arrangement in a DASD for providingsignal connections with MR transducer heads that maintains adequatenoise rejection for the read signal.

SUMMARY OF THE INVENTION

It is a principal object of the present invention to provide anapparatus for providing signal connections with MR transducer heads in adirect access storage device that overcomes many of the disadvantages ofprior art arrangements.

In brief, the objects and advantages of the present invention areachieved by a direct access storage device including at least one diskmounted for rotation about an axis and having opposed disk surfaces forstoring data. A magneto-resistive (MR) transducer head is mounted formovement across each respective disk surface for writing to and forreading data signals from the disk surface. Each MR transducer headincludes a write element and a read element. A preamplifier, associatedwith the MR transducer heads, amplifies read and write signals of theread element and the write element. A flex cable couples the read andwrite signals between the preamplifier and the MR transducer heads. Theflex cable includes a common read return signal line for each sequentialpair of the MR transducer heads.

BRIEF DESCRIPTION OF THE DRAWING

The present invention together with the above and other objects andadvantages may best be understood from the following detaileddescription of the preferred embodiment of the invention illustrated inthe drawings, wherein:

FIG. 1 is a schematic and block diagram of a data storage disk fileembodying the present invention;

FIG. 2 is a diagram showing tracks and sectors of a data disk surface ofthe data storage disk file of FIG. 1;

FIG. 3 is a block diagram representation illustrating magneto-resistivetransducer head signal apparatus according to the present invention inthe data storage disk file of FIG. 1; and

FIG. 4 is a block diagram representation illustrating a prior artconnection arrangement for magneto-resistive transducer heads.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 there is shown a partly schematic block diagram of parts of adata storage disk file 10 including a data storage medium generallydesignated as 12 and a control unit generally designated as 14. In thepreferred embodiment of this invention, the data storage medium 12 isembodied in a rigid magnetic disk drive unit 12, although othermechanically moving memory configurations may be used. Unit 12 isillustrated in simplified form sufficient for an understanding of thepresent invention because the utility of the present invention is notlimited to the details of a particular drive unit construction.

Referring now to FIGS. 1 and 2, disk drive unit 12 includes a stack 16of disks 18 having magnetic surfaces. Data disks 18 include a layer ofmagnetic material on opposed disk surfaces 26. Unit 12 includes aselected number of the double-sided data disks 18 to provide a selectedstorage capacity as indicated in FIG. 1 numbered from SURFACE 0 throughSURFACE N. Numerous data information tracks or cylinders 28 are arrayedin a concentric pattern in the magnetic medium of each disk surface 26of data disks 18. The data information tracks 28 are disposed atpredetermined positions relative to servo reference tracks, such as R0illustrated in FIG. 2. A data cylinder includes a set of correspondingdata information tracks 28 for the data SURFACES 0-N. For example, 951data cylinders can be included in the disk surfaces 26 numbered from0-950 as indicated in FIG. 2. Each data information track 28 includesmultiple data sectors 30 equally spaced around the cylinder; forexample, 96 data sectors numbered 0-95.

The disks 18 are mounted in parallel for simultaneous rotation on and byan integrated spindle and motor assembly 32. The data information tracks28 on each disk 18 are read and/or written to by a corresponding datatransducer head 34 movable across the disk surface. Transducer heads 34are carried by arms 38 ganged together on an actuator 40 forsimultaneous pivotal movement about an axis. Actuator 40 includes anextension 42 driven in a pivotal motion by a head drive motor, which isrepresented in block form as feature 44. Although several drivearrangements are possible, motor 44 typically includes a coil 46cooperating with a magnet and core assembly (not seen) operativelycontrolled for moving the transducer heads 34 in synchronism in a radialdirection in order to position the heads in registration with thecylinders 28 to be followed.

Data utilization device 14 typically includes an interface or fileprocessor 50 that controls transfer of data to be stored in the datasectors 30 of disks 18 for subsequent access and use. A servo processor52 is coupled between the interface processor 50, the motors 32 and 44and the data transducer heads 34. The servo processor 52 controls theoperations of moving the heads 34 into registration with a target orselected data LBA and of transferring data under the control of theinterface processor 50.

Disk access is operatively controlled by the servo processor 52. Motor32 is operated to rotate the disk stack 16. The servo processor 52employs servo control operations to move the data heads 34 radially withrespect to the rotating disks 18 by the head drive motor 44 toselectively align each of the data transducer heads with a specificradial position of the cylinder 28 where data is to be read or written.

Referring now to FIG. 3, there is shown a pair of sequential transducerheads 34 of the disk file 10 together with signal apparatus arranged inaccordance with the invention. Transducer heads 34 are magneto-resistive(MR) heads labeled MR HEAD 1 and MR HEAD 2. Each MR head 34 includes aMR read element and a write element. Signal connections from apreamplifier 60 are provided by a flex cable 62 via a respective twistedpair of head suspension wires to each MR read element and write element.A pair of write signal lines in the flex cable 62 are required for eachwrite element of MR heads 34. In accordance with the invention, flexcable 62 includes a single read return signal conductor or line labeledCOMMON-READ-RETURN utilized for each sequential pair of MR heads 34 inthe disk file 10. The COMMON-READ-RETURN extends from a point where theread head suspension wires attach to the flex cable 62.

A single ended preamplifier can be used for the preamplifier 60 whichallows the read return signal line from the MR read element to be at areference potential, typically ground potential. Reference potential forthe COMMON-READ-RETURN signal line connection to the preamplifier 60 isillustrated at an I/O input by a negative (-) label. The read signalline connection to the preamplifier 60 is illustrated at an I/O input bya positive (+) label. In the disk file 10, the COMMON-READ-RETURN signalline is required to maintain adequate noise rejection for the readsignal. Keeping the MR read signal line and MR COMMON-READ-RETURN signalline close together in the flex cable 62 increases the mutualinductance. As illustrated, the COMMON-READ-RETURN signal line isdisposed between the respective read signal lines for MR heads 1 and 2to maintain adequate mutual inductance for common mode noise rejection.

As shown in FIG. 3, the number of input/output (I/O) connections of theflex cable 62 is reduced by one for a disk file including two MR heads34 and preamplifier 60. Reducing the number of signal lines on flexcable 62 provides a number of advantages including but not limited to, areduction of the flex cable width and/or a reduction of preamplifier I/Oor allowing a wider line width on the flex cable 62. In the preferredembodiment, the preamplifier 60 exists as a single integrated circuitchip. However, the read and write circuits are generally separate; itshould be understood that the read and write preamplifiers can beprovided on separate integrated circuit chips.

In the disk file 10 that includes a number of MR heads 34 equal to N,the number of required read signal lines is reduced, by N/2 where N isan even number of MR heads or by (N-1)/2 where N is an odd number of MRheads, as compared to the prior art arrangement of FIG. 4. Similarly,the required number of I/O connections of preamplifier 60 can bereduced.

While the invention has been described with reference to details of theillustrated embodiment, these details are not intended to limit thescope of the invention as defined in the appended claims.

What is claimed is:
 1. A direct access storage device comprising:atleast one disk mounted for rotation about an axis and having opposeddisk surfaces for storing data; a plurality of magneto-resistive (MR)transducer means mounted for movement across respective disk surfaces,each for writing to and for reading data signals from a respective disksurface; each said MR transducer means including a write element and aread element, preamplifier means, associated with said MR transducermeans, for amplifying read and write signals; and flex cable means forcoupling said read and write signals between said preamplifier means andsaid MR transducer means, said flex cable means including two writesignal lines coupled to each said write element of said MR transducermeans, a read signal line coupled to each said read element of said MRtransducer means, and a common read return signal line simultaneouslyconnected to each sequential pair of said read elements of said MRtransducer means and directly connected to said preamplifier means.
 2. Adirect access storage device as recited in claim 1 wherein saidpreamplifier means is a single-ended preamplifier and said common readreturn signal line is at a reference potential.
 3. A direct accessstorage device as recited in claim 1 including a number N of sequentialMR transducing means and wherein said flex cable means includes N/2common read return lines, where N is an even number.
 4. A direct accessstorage device as recited in claim 1 including a number N of sequentialMR transducing means and wherein said flex cable means includes (N-1)/2common read return signal lines, where N is an odd number; and whereinsaid flex cable means includes N/2 common read return signal lines,where N is an even number.
 5. A direct access storage devicecomprising:a plurality of disks mounted in a stack for simultaneousrotation about an axis and each disk having opposed disk surfaces forstoring data; a plurality of magneto-resistive (MR) transducer heads,each said MR transducer head mounted for movement across a respectivedisk surface and including a write element for writing to and a readelement for reading data signals from said respective disk surface;preamplifier means, associated with said MR transducer heads, foramplifying read and write signals; and flex cable means for couplingsaid read and write signals between said preamplifier means and said MRread and write elements, said flex cable means including two writesignal lines coupled to each said write element of said MR transducerheads, a read signal line coupled to each said read element of said MRtransducer heads, and a common read return signal line simultaneouslyconnected to said read elements of each sequential pair of said MRtransducer heads in said stack of disks and directly connected to saidpreamplifier means.
 6. A direct access storage device as recited inclaim 5 wherein said common read return signal line extends between andgenerally parallel with a pair of said read signal lines of eachsequential pair of said MR transducer heads.
 7. A direct access storagedevice as recited in claim 5 wherein said common read return signal lineis at a reference potential.